(3) As in the development of personal morality, the hostility of inanimate nature, coupled with the urgency of inner needs, has also played its part in the socialization of man. The satisfying of hunger, protection against storm, flood, and other physical calamities, is greatly forwarded by cooperation. The rearing of a shelter, for example, that shall be at all comfortable and secure, demands the labor of several. With the development of civilization, mutual assistance and the division of labor become more and more imperative. As man developed more and more into a reflective animal, the comprehension of these advantages became clearer and clearer to him. Resentment against mere individualism grew keener; and any member whose laziness or passions led him to pull apart from the common good had to incur the anger of his fellows. Under these three heads--the selection of the maternal instinct, with its potentialities of universal sympathy, through the struggle between individuals; the selection of the various powers of loyalty and cooperation through the struggle between groups; and the production of cooperative habits through the struggle with inanimate nature-we may group the causes of social morality in man. How has morality been fostered by the tribe? Social morality, like personal morality, is passed on from generation to generation by heredity and by imitation. Both, in historic man, are also deliberately cultivated by the tribe. We have discriminated between the two aspects of morality for theoretic reasons which will later become apparent; but no discrimination is possible or needful for the savage. Courage and prudence and industriousness and temperance in its members are assets of the tribe, and are included among its requirements. We shall now consider in what ways the group brings pressure to bear upon the individual and influences his moral development.